Initiator system for anionic polymerizations

ABSTRACT

This invention is based upon the discovery of certain anionic initiator systems can be used to initiate the solution polymerization of conjugated diolefin monomers into rubbery polymers having a low vinyl content. For instance, such initiator systems can be used in the copolymerization of styrene and isoprene to produce low vinyl styrene-isoprene rubber having a random distribution of repeat units that are derived from styrene. These initiator systems are comprised of (a) a lithium initiator and (b) a member selected from the group consisting of (1) a sodium alkoxide, (2) a sodium salt of a sulfonic acid, and (3) a sodium salt of a glycol ether. It is important for the initiator system to be free of polar modifiers, such as Lewis bases. The subject invention more specifically discloses an initiator system which is comprised of (a) a lithium initiator and (b) a member selected from the group consisting of (1) a sodium alkoxide, (2) a sodium salt of a sulfonic acid, and (3) a sodium salt of a glycol ether, wherein said initiator system is void of polar modifiers. The present invention also discloses a process for preparing a rubbery polymer having a low vinyl content which comprises: polymerizing at least one diene monomer with a lithium initiator at a temperature which is within the range of about 5° C. to about 180° C. in the presence of a member selected from the group consisting of (1) a sodium alkoxide, (2) a sodium salt of a sulfonic acid, and (3) a sodium salt of a glycol ether, and wherein the process is conducted in the absence of polar modifiers.

BACKGROUND OF THE INVENTION

[0001] Good traction characteristics on both dry and wet surfaces is ahighly desirable characteristic of tires to possess. However, it hastraditionally been very difficult to improve the tractioncharacteristics of a tire without compromising its rolling resistanceand tread wear. Low rolling resistance is important because good fueleconomy is virtually always an important consideration. Good tread wearis also an important consideration because it is generally the mostimportant factor that determines the life of the tire.

[0002] To a large extent the traction, tread wear, and rollingresistance of a tire is dependent on the dynamic viscoelastic propertiesof the elastomers utilized in making the tire tread. In order to reducethe rolling resistance of a tire, rubbers having a high rebound havetraditionally been utilized in making the tire's tread. On the otherhand, in order to increase the wet skid resistance of a tire, rubberswhich undergo a large energy loss have generally been utilized in thetire's tread. In order to balance these two viscoelasticallyinconsistent properties, mixtures of various types of synthetic andnatural rubber are normally utilized in tire treads. For instancevarious mixtures of styrene-butadiene rubber and polybutadiene rubberare commonly used as a rubber material for automobile tire treads.However, such blends are not totally satisfactory for all purposes.

[0003] The inclusion of styrene-butadiene rubber (SBR) in tire treadformulations can significantly improve the traction characteristics oftires made therewith. However, styrene is a relatively expensive monomerand the inclusion of SBR is tire tread formulations leads to increasedcosts.

[0004] Carbon black is generally included in rubber compositions thatare employed in making tires and most other rubber articles. It isdesirable to attain the best possible dispersion of the carbon blackthroughout the rubber to attain optimized properties. It is also highlydesirable to improve the interaction between the carbon black and therubber. By improving the affinity of the rubber compound to the carbonblack, physical properties can be improved. Silica can also be includedin tire tread formulations to improve rolling resistance.

[0005] U.S. Pat. No. 4,843,120 discloses that tires having improvedperformance characteristics can be prepared by utilizing rubberypolymers having multiple glass transition temperatures as the treadrubber These rubbery polymers having multiple glass transitiontemperatures exhibit a first glass transition temperature which iswithin the range of about −110° C. to −20° C. and exhibit a second glasstransition temperature which is within the range of about −50° C. to 0°C. According to U.S. Pat. No. 4,843,120, these polymers are made bypolymerizing at least one conjugated diolefin monomer in a firstreaction zone at a temperature and under conditions sufficient toproduce a first polymeric segment having a glass transition temperaturewhich is between −110° C. and −20° C. and subsequently continuing saidpolymerization in a second reaction zone at a temperature and underconditions sufficient to produce a second polymeric segment having aglass transition temperature which is between −20° C. and 20° C. Suchpolymerizations are normally catalyzed with an organolithium catalystand are normally carried out in an inert organic solvent.

[0006] U.S. Pat. No. 5,137,998 discloses a process for preparing arubbery terpolymer of styrene, isoprene, and butadiene having multipleglass transition temperatures and having an excellent combination ofproperties for use in making tire treads which comprises:terpolymerizing styrene, isoprene and 1,3-butadiene in an organicsolvent at a temperature of no more than about 40° C. in the presence of(a) at least one member selected from the group consisting oftripiperidino phosphine oxide and alkali metal alkoxides and (b) anorganolithium compound.

[0007] U.S. Pat. No. 5,047,483 discloses a pneumatic tire having anouter circumferential tread where said tread is a sulfur cured rubbercomposition comprised of, based on 100 parts by weight rubber (phr), (A)about 10 to about 90 parts by weight of a styrene, isoprene, butadieneterpolymer rubber (SIBR), and (B) about 70 to about 30 weight percent ofat least one of cis 1,4-polyisoprene rubber and cis 1,4-polybutadienerubber wherein said SIBR rubber is comprised of (1) about 10 to about 35weight percent bound styrene, (2) about 30 to about 50 weight percentbound isoprene and (3) about 30 to about 40 weight percent boundbutadiene and is characterized by having a single glass transitiontemperature (Tg) which is in the range of about −10° C. to about −40° C.and, further the said bound butadiene structure contains about 30 toabout 40 percent 1,2-vinyl units, the said bound isoprene structurecontains about 10 to about 30 percent 3,4-units, and the sum of thepercent 1,2-vinyl units of the bound butadiene and the percent 3,4-unitsof the bound isoprene is in the range of about 40 to about 70 percent.

[0008] U.S. Pat. No. 5,272,220 discloses a styrene-isoprene-butadienerubber which is particularly valuable for use in making truck tiretreads which exhibit improved rolling resistance and tread wearcharacteristics, said rubber being comprised of repeat units which arederived from about 5 weight percent to about 20 weight percent styrene,from about 7 weight percent to about 35 weight percent isoprene, andfrom about 55 weight percent to about 88 weight percent 1,3-butadiene,wherein the repeat units derived from styrene, isoprene and1,3-butadiene are in essentially random order, wherein from about 25% toabout 40% of the repeat units derived from the 1,3-butadiene are of thecis-microstructure, wherein from about 40% to about 60% of the repeatunits derived from the 1,3-butadiene are of the trans-microstructure,wherein from about 5% to about 25% of the repeat units derived from the1,3-butadiene are of the vinyl-microstructure, wherein from about 75% toabout 90% of the repeat units derived from the isoprene are of the1,4-microstructure, wherein from about 10% to about 25% of the repeatunits derived from the isoprene are of the 3,4-microstructure, whereinthe rubber has a glass transition temperature which is within the rangeof about −90° C. to about −70° C., wherein the rubber has a numberaverage molecular weight which is within the range of about 150,000 toabout 400,000, wherein the rubber has a weight average molecular weightof about 300,000 to about 800,000, and wherein the rubber has aninhomogeneity which is within the range of about 0.5 to about 1.5.

[0009] U.S. Pat. No. 5,239,009 reveals a process for preparing a rubberypolymer which comprises: (a) polymerizing a conjugated diene monomerwith a lithium initiator in the substantial absence of polar modifiersat a temperature which is within the range of about 5° C. to about 100°C. to produce a living polydiene segment having a number averagemolecular weight which is within the range of about 25,000 to about350,000; and (b) utilizing the living polydiene segment to initiate theterpolymerization of 1,3-butadiene, isoprene, and styrene, wherein theterpolymerization is conducted in the presence of at least one polarmodifier at a temperature which is within the range of about 5° C. toabout 70° C. to produce a final segment which is comprised of repeatunits which are derived from 1,3-butadiene, isoprene, and styrene,wherein the final segment has a number average molecular weight which iswithin the range of about 25,000 to about 350,000. The rubbery polymermade by this process is reported to be useful for improving the wet skidresistance and traction characteristics of tires without sacrificingtread wear or rolling resistance.

[0010] U.S. Pat. No. 5,061,765 discloses isoprene-butadiene copolymershaving high vinyl contents which can be employed in building tires whichhave improved traction, rolling resistance, and abrasion resistance.These high vinyl isoprene-butadiene rubbers are synthesized bycopolymerizing 1,3-butadiene monomer and isoprene monomer in an organicsolvent at a temperature which is within the range of about −10° C. toabout 100° C. in the presence of a catalyst system which is comprised of(a) an organoiron compound, (b) an organoaluminum compound, (c) achelating aromatic amine, and (d) a protonic compound; wherein the molarratio of the chelating amine to the organoiron compound is within therange of about 0.1:1 to about 1:1, wherein the molar ratio of theorganoaluminum compound to the organoiron compound is within the rangeof about 5:1 to about 200:1, and herein the molar ratio of the protoniccompound to the organoaluminum compound is within the range of about0.001:1 to about 0.2:1.

[0011] U.S. Pat. No. 5,405,927 discloses an isoprene-butadiene rubberwhich is particularly valuable for use in making truck tire treads, saidrubber being comprised of repeat units which are derived from about 20weight percent to about 50 weight percent isoprene and from about 50weight percent to about 80 weight percent 1,3-butadiene, wherein therepeat units derived from isoprene and 1,3-butadiene are in essentiallyrandom order, wherein from about 3% to about 10% of the repeat units insaid rubber are 1,2-polybutadiene units, wherein from about 50% to about70% of the repeat units in said rubber are 1,4-polybutadiene units,wherein from about 1% to about 4% of the repeat units in said rubber are3,4-polyisoprene units, wherein from about 25% to about 40% of therepeat units in the polymer are 1,4-polyisoprene units, wherein therubber has a glass transition temperature which is within the range ofabout −90° C. to about −75° C., and wherein the rubber has a Mooneyviscosity which is within the range of about 55 to about 140.

[0012] U.S. Pat. No. 4,139,690 discloses a process for preparingconjugated diene polymers by either polymerization of one or moremonomers selected from a group of conjugated diene compounds orcopolymerization of a conjugated diene compound with an alkenyl aromaticcompound, using an organolithium initiator in a hydrocarbon solvent,characterized in that the polymerization is carried out in the presenceof (1) one or more anionic surface active agent having a group SO₃M or—OSO₃M (where M is an alkali metal) and (2) one or more Lewis bases.

[0013] U.S. Pat. No. 5,654,384 discloses a process for preparing highvinyl polybutadiene rubber which comprises polymerizing 1,3-butadienemonomer with a lithium initiator at a temperature which is within therange of about 50° C. to about 100° C. in the presence of a sodiumalkoxide and a polar modifier, wherein the molar ratio of the sodiumalkoxide to the polar modifier is within the range of about 0.1:1 toabout 10:1; and wherein the molar ratio of the sodium alkoxide to thelithium initiator is within the range of about 0.05:1 to about 10:1. Byutilizing a combination of sodium alkoxide and a conventional polarmodifier, such as an amine or an ether, the rate of polymerizationinitiated with organolithium compounds can be greatly increased with theglass transition temperature of the polymer produced also beingsubstantially increased. The rubbers synthesized using such catalystsystems also exhibit excellent traction properties when compounded intotire tread formulations. This is attributable to the uniquemacrostructure (random branching) of the rubbers made with such catalystsystems.

[0014] U.S. Pat. Nos. 5,620,939, 5,627,237, and 5,677,402 also disclosethe use of sodium salts of saturated aliphatic alcohols, such a sodiumt-amylate, as modifiers for lithium initiated solution polymerizations

[0015] U.S. Pat. No. 6,140,434 discloses a process for preparing arubbery polymer having a high vinyl content which comprises:polymerizing at least one diene monomer with a lithium initiator at atemperature which is within the range of about 5° C. to about 100° C. inthe presence of a metal salt of a cyclic alcohol and a polar modifier,wherein the molar ratio of the metal salt of the cyclic alcohol to thepolar modifier is within the range of about 0.1:1 to about 10:1; andwherein the molar ratio of the metal salt of the cyclic alcohol to thelithium initiator is within the range of about 0.05:1 to about 10:1.U.S. Pat. No. 6,140,434 is based upon the discovery that metal salts ofcyclic alcohols will act as highly effective modifiers that do notco-distill with hexane or form compounds during steam stripping whichco-distill with hexane. The use of metal salts of cyclic alcoholsaccordingly solves the problem of recycle stream contamination.Additionally, these modifiers provide similar modification efficienciesto sodium t-amylate. Since the boiling points of these metal salts ofcyclic alcohols are very high, they do not co-distill with hexane andcontaminate recycle streams. Metal salts of cyclic alcohols are alsoconsidered to be environmentally safe. In fact, sodium mentholate isused as a food additive.

SUMMARY OF THE INVENTION

[0016] This invention is based upon the discovery of certain anionicinitiator systems can be used to initiate the polymerization ofconjugated diolefin monomers into rubbery polymers having a low vinylcontent. For instance, such initiator systems can be used in thecopolymerization of styrene and isoprene to produce low vinylstyrene-isoprene rubber having a random distribution of repeat unitsthat are derived from styrene.

[0017] The initiator systems of this invention are comprised of (a) alithium initiator and (b) a member selected from the group consisting of(1) a sodium alkoxide, (2) a sodium salt of a sulfonic acid, and (3) asodium salt of a glycol ether. It is important for the initiator systemto be free of polar modifiers, such as Lewis bases.

[0018] The subject invention more specifically discloses an initiatorsystem which is comprised of (a) a lithium initiator and (b) a memberselected from the group consisting of (1) a sodium alkoxide, (2) asodium salt of a sulfonic acid, and (3) a sodium salt of a glycol ether,wherein said initiator system is void of polar modifiers.

[0019] The present invention also discloses a process for preparing arubbery polymer having a low vinyl content which comprises: polymerizingat least one diene monomer with a lithium initiator at a temperaturewhich is within the range of about 0° C. to about 180° C. in thepresence of a member selected from the group consisting of (1) a sodiumalkoxide, (2) a sodium salt of a sulfonic acid, and (3) a sodium salt ofa glycol ether, and wherein the process is conducted in the absence ofpolar modifiers.

[0020] The initiator systems of this invention have proven to be ofparticular value in the copolymerization of styrene and isoprene intolow vinyl styrene-isoprene rubber having a random distribution of repeatunits that are derived from styrene. The subject invention accordinglyalso discloses a process for preparing a styrene-isoprene rubber havinga low vinyl content and a random distribution of repeat units that arederived from styrene which comprises: copolymerizing styrene andisoprene with a lithium initiator at a temperature which is within therange of about 0° C. to about 180° C. in the presence of a memberselected from the group consisting of (1) a sodium alkoxide, (2) asodium salt of a sulfonic acid, and (3) a sodium salt of a glycol ether,and wherein the process is conducted in the absence of polar modifiers.

DETAILED DESCRIPTION OF THE INVENTION

[0021] The polymerizations of this invention are normally carried out assolution polymerizations in an inert organic medium utilizing a lithiumcatalyst. However, a member selected from the group consisting of (1) asodium alkoxide, (2) a sodium salt of a sulfonic acid, and (3) a sodiumsalt of a glycol ether can also be employed in accordance with thisinvention as modifiers for bulk polymerizations or vapor phasepolymerizations. In order to attain a low vinyl content it is importantof conduct the polymerization is the absence of polar modifiers, such asLewis bases.

[0022] The rubbery polymers synthesized using the initiator systems ofthis invention can be made by the homopolymerization of a conjugateddiolefin monomer or by the copolymerization of a conjugated diolefinmonomer with a vinyl aromatic monomer. It is, of course, also possibleto make rubbery polymers by polymerizing a mixture of conjugateddiolefin monomers with one or more ethylenically unsaturated monomers,such as vinyl aromatic monomers. The conjugated diolefin monomers whichcan be utilized in the synthesis of rubbery polymers in accordance withthis invention generally contain from 4 to 12 carbon atoms. Thosecontaining from 4 to 8 carbon atoms are generally preferred forcommercial purposes. For similar reasons, 1,3-butadiene and isoprene arethe most commonly utilized conjugated diolefin monomers. Some additionalconjugated diolefin monomers that can be utilized include2,3-dimethyl-1,3-butadiene, piperylene, 3-butyl-1,3-octadiene,2-phenyl-1,3-butadiene, and the like, alone or in admixture.

[0023] Some representative examples of ethylenically unsaturatedmonomers that can potentially be copolymerized into rubbery polymersusing the modifiers of this invention include alkyl acrylates, such asmethyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate andthe like; vinylidene monomers having one or more terminal CH2═CH—groups; vinyl aromatics such as styrene, α-methylstyrene, bromostyrene,chlorostyrene, fluorostyrene and the like; a-olefins such as ethylene,propylene, 1-butene and the like; vinyl halides, such as vinylbromide,chloroethane (vinylchloride), vinylfluoride, vinyliodide,1,2-dibromoethene, 1,1-dichloroethene (vinylidene chloride),1,2-dichloroethene and the like; vinyl esters, such as vinyl acetate;α,β-olefinically unsaturated nitrites, such as acrylonitrile andmethacrylonitrile; α,β-olefinically unsaturated amides, such asacrylamide, N-methyl acrylamide, N,N-dimethylacrylamide, methacrylamideand the like.

[0024] Rubbery polymers which are copolymers of one or more dienemonomers with one or more other ethylenically unsaturated monomers willnormally contain from about 50 weight percent to about 99 weight percentconjugated diolefin monomers and from about 1 weight percent to about 50weight percent of the other ethylenically unsaturated monomers inaddition to the conjugated diolefin monomers. For example, copolymers ofconjugated diolefin monomers with vinylaromatic monomers, such asstyrene-butadiene rubbers which contain from 50 to 95 weight percentconjugated diolefin monomers and from 5 to 50 weight percentvinylaromatic monomers, are useful in many applications.

[0025] Vinyl aromatic monomers are probably the most important group ofethylenically unsaturated monomers that are commonly incorporated intopolydienes. Such vinyl aromatic monomers are, of course, selected so asto be copolymerizable with the conjugated diolefin monomers beingutilized. Generally, any vinyl aromatic monomer which is known topolymerize with organolithium initiators can be used. Such vinylaromatic monomers typically contain from 8 to 20 carbon atoms. Usually,the vinyl aromatic monomer will contain from 8 to 14 carbon atoms. Themost widely used vinyl aromatic monomer is styrene. Some examples ofvinyl aromatic monomers that can be utilized include styrene,1-vinylnaphthalene, 2-vinylnaphthalene, (α-methylstyrene,4-phenylstyrene, 3-methylstyrene and the like.

[0026] Some representative examples of rubbery polymers which cansynthesized in accordance with this invention include polybutadiene,polyisoprene, styrene-butadiene rubber (SBR), (α-methylstyrene-butadienerubber, α-methylstyrene-isoprene rubber, styrene-isoprene-butadienerubber (SIBR), styrene-isoprene rubber (SIR), isoprene-butadiene rubber(IBR), (α-methylstyrene-isoprene-butadiene rubber andα-methylstyrene-styrene-isoprene-butadiene rubber. Low vinylstyrene-isoprene rubber having a random distribution of repeat unitsthat are derived from styrene has proven to be particularly importantfor utilization in making tire tread compounds.

[0027] In solution polymerizations the inert organic medium which isutilized as the solvent will typically be a hydrocarbon which is liquidat ambient temperatures which can be one or more aromatic, paraffinic orcycloparaffinic compounds These solvents will normally contain from 4 to10 carbon atoms per molecule and will be liquids under the conditions ofthe polymerization. It is, of course, important for the solvent selectedto be inert. The term “inert” as used herein means that the solvent doesnot interfere with the polymerization reaction or react with thepolymers made thereby. Some representative examples of suitable organicsolvents include pentane, isooctane, cyclohexane, normal hexane,benzene, toluene, xylene, ethylbenzene and the like, alone or inadmixture. Saturated aliphatic solvents, such as cyclohexane and normalhexane, are most preferred.

[0028] The lithium initiators that are used in the initiator systems ofthis invention are typically organolithium compounds. The organolithiumcompounds which are preferred can be represented by the formula: R—Li,wherein R represents a hydrocarbyl radical containing from 1 to about 20carbon atoms. Generally, such monofunctional organolithium compoundswill contain from 1 to about 10 carbon atoms. Some representativeexamples of organolithium compounds which can be employed includemethyllithium, ethyllithium, isopropyllithium, n-butyllithium,sec-butyllithium, n-octyllithium, tert-octyllithium, n-decyllithium,phenyllithium, 1-napthyllithium, 4-butylphenyllithium, p-tolyllithium,1-naphthyllithium, 4-butylphenyllithium, p-tolyllithium,4-phenylbutyllithium, cyclohexyllithium, 4-butylcyclohexyllithium, and4-cyclohexylbutyllithium. Organo monolithium compounds, such asalkyllithium compounds and aryllithium compounds, are usually employed.Some representative examples of preferred organo monolithium compoundsthat can be utilized include ethylaluminum, isopropylaluminum,n-butyllithium, secondary-butyllithium, normal-hexyllithium,tertiary-octyllithium, phenyllithium, 2-napthyllithium,4-butylphenyllithium, 4-phenylbutyllithium, cyclohexyllithium, and thelike. Normal-butyllithium and secondary-butyllithium are highlypreferred lithium initiators.

[0029] The amount of lithium catalyst utilized will vary from oneorganolithium compound to another and with the molecular weight that isdesired for the rubber being synthesized. As a general rule, in allanionic polymerizations the molecular weight (Mooney viscosity) of thepolymer produced is inversely proportional to the amount of catalystutilized. Normally, from about 0.01 phm (parts per hundred parts byweight of monomer) to 1 phm of the lithium catalyst will be employed. Inmost cases, from 0.01 phm to 0.1 phm of the lithium catalyst will beemployed with it being preferred to utilize 0.025 phm to 0.07 phm of thelithium catalyst.

[0030] Typically, from about 5 weight percent to about 35 weight percentof the monomer will be charged into the polymerization medium (basedupon the total weight of the polymerization medium including the organicsolvent and monomer). In most cases, it will be preferred for thepolymerization medium to contain from about 10 weight percent to about30 weight percent monomer. It is typically more preferred for thepolymerization medium to contain from about 20 weight percent to about25 weight percent monomer.

[0031] The polymerization temperature will normally be within the rangeof about 0° C. to about 180° C. The polymerization temperature willnormally be within the range of about 5° C. to about 100° C. Forpractical reasons and to attain the desired microstructure thepolymerization temperature will preferably be within the range of about40° C. to about 90° C. Polymerization temperatures within the range ofabout 60° C. to about 90° C. are most preferred. The microstructure ofthe rubbery polymer is somewhat dependent upon the polymerizationtemperature. For example, it is known that higher temperatures result inlower vinyl contents (lower levels of 1,2-microstructure). Accordingly,the polymerization temperature will be determined with the desiredmicrostructure of the polydiene rubber being synthesized being kept inmind.

[0032] The polymerization is allowed to continue until essentially allof the monomer has been exhausted. In other words, the polymerization isallowed to run to completion. Since a lithium catalyst is employed topolymerize the monomer, a living polymer is produced. The living polymersynthesized will have a number average molecular weight that is withinthe range of about 25,000 to about 700,000. The rubber synthesized willmore typically have a number average molecular weight that is within therange of about 150,000 to about 400,000.

[0033] To maintain a low vinyl content the polymerization is carried outin the absence of polar modifiers. Ethers and tertiary amines which actas Lewis bases are representative examples of polar modifiers that mustbe avoided. Some specific examples of polar modifiers include diethylether, di-n-propyl ether, diisopropyl ether, di-n-butyl ether,tetrahydrofuran, dioxane, ethylene glycol dimethyl ether, ethyleneglycol diethyl ether, diethylene glycol dimethyl ether, diethyleneglycol diethyl ether, triethylene glycol dimethyl ether, trimethylamine,triethylamine, N,N,N′,N′-tetramethylethylenediamine, N-methylmorpholine, N-ethyl morpholine, N-phenyl morpholine and the like.

[0034] The polymerization medium should also be void of modifier such as1,2,3-trialkoxybenzenes or a 1,2,4-trialkoxybenzenes. Somerepresentative examples of 1,2,3-trialkoxybenzenes include1,2,3-trimethoxybenzene, 1,2,3-triethoxybenzene, 1,2,3-tributoxybenzene,1,2,3-trihexoxybenzene, 4,5,6-trimethyl-1,2,3-trimethoxybenzene,4,5,6-tri-n-pentyl-1,2,3-triethoxybenzene,5-methyl-1,2,3-trimethoxybenzene, and 5-propyl-1,2,3-trimethoxybenzene.Some representative examples of 1,2,4-trialkoxybenzenes that can be usedinclude 1,2,4-trimethoxybenzene, 1,2,4-triethoxybenzene,1,2,4-tributoxybenzene, 1,2,4-tripentoxybenzene,3,5,6-trimethyl-1,2,4-trimethoxybenzene,5-propyl-1,2,4-trimethoxybenzene, and3,5-dimethyl-1,2,4-trimethoxybenzene. Some additional examples ofmodifiers that should be avoided include dipiperidinoethane,dipyrrolidinoethane, tetramethylethylene diamine, diethylene glycol,dimethyl ether and tetrahydrofuran. U.S. Pat. No. 4,022,959 describesethers and tertiary amines that can as polar modifiers in greaterdetail. The 1,2,3-trialkoxybenzenes and 1,2,4-trialkoxybenzenes that actas modifiers are described in greater detail in U.S. Pat. No. 4,696,986.The teachings of U.S. Pat. Nos. 4,022,959 and 4,696,986 are incorporatedherein by reference in their entirety.

[0035] The sodium alkoxides that can be utilized in the initiatorsystems of this invention will normally be of the formula NaOR, whereinR is an alkyl group containing from about 2 to about 12 carbon atoms.The sodium metal alkoxide will typically contain from about 2 to about12 carbon atoms. It is generally preferred for the sodium alkoxide tocontain from about 3 to about 8 carbon atoms. It is generally mostpreferred for the sodium alkoxide to contain from about 4 to about 6carbon atoms. Sodium t-amyloxide (sodium t-pentoxide) is arepresentative example of a preferred sodium alkoxides that can beutilized in the modifier systems of this invention.

[0036] The molar ratio of sodium alkoxide to the lithium initiator willnormally be within the range of about 0.01:1 to about 20:1. It isgenerally preferred for the molar ratio of sodium alkoxide to thelithium initiator to be within the range of about 0.05:1 to about 10:1.It is generally more preferred for the molar ratio of the sodiumalkoxide to the lithium initiator to be within the range of about 0.2:1to about 3:1.

[0037] The sodium salts of the sulfonic acids that can be used in theinitiator systems of this invention will normally contain from about 6to about 30 carbon atoms. The sodium salt of the sulfonic acid willtypically be a sodium salt of alkylaromatic sulfonates of the structuralformula:

[0038] wherein R represents an alkyl group containing from 1 to about 20carbon atoms and wherein A represents an aromatic ring. The alkyl groupwill preferably contain from about 6 to about 18 carbon atoms. Thearomatic ring will typically be a benzene ring, naphthalene ring,anthracene ring, pentalene ring, heptalene ring, acenaphthylene ring,phenalene ring, phenanthrene ring, fluoranthene ring, acephenanthrylenering, aceanthrylene ring, triphenylene ring, pyrene ring, chrysene ring,naphthacene ring, pentacene ring, hexacene ring, or a similar aromaticring structure. The aromatic ring will typically be a benzene ring, anaphthalene ring or an anthracene ring. It is critical for initiatorsystems that contain a sodium salt of a sulfonic acid to be free ofwater and for polymerizations that utilize such initiator systems to beconducted in the absence of water.

[0039] Sodium salts of alkylbenzene sulfonates are a highly preferredclass of modifier. Sodium salts of alkylbenzene sulfonates have thestructural formula:

[0040] wherein R represents an alkyl group containing from 1 to about 20carbon atoms. It is preferred for the alkyl group to contain from about8 to about 14 carbon atoms. It is highly preferred for the sodium saltof the aklylbenzene sulfonate to be sodium dodecylbenzene sulfonate.

[0041] Sodium dodecylbenzene sulfonate from commercial sources normallycontains a small amount of residual water and is accordingly notsuitable for use in the polymerizations of this invention. However,water-free sodium dodecylbenzene sulfonate can be made by reactingdodecyl benzene sulfonic acid with dry sodium hydroxide pellets in anaromatic solvent, such as toluene or ethyl benzene. This reaction willnormally be carried out utilizing a molar excess of sodium hydroxide. Infact, the molar ratio of sodium hydroxide to dodecyl benzene sulfonicacid will typically be within the range of about 3:1 to about 5:1. It iscritical to reflux the aromatic reaction medium to remove any residualwater.

[0042] The molar ratio of the sodium salt of the sulfonic acid to thelithium initiator will normally be within the range of about 0.1:1 toabout 1:1. It is generally preferred for the molar ratio of the sodiumsalt of the sulfonic acid to the lithium initiator to be within therange of about 0.2:1 to about 0.6:1. It is generally more preferred forthe molar ratio of the sodium salt of the sulfonic acid to the lithiuminitiator to be within the range of about 0.2:1 to about 0.4:1. As ageneral rule, the ratio of the sodium salt of the sulfonic acid to thelithium initiator required to attain a totally random sequencedistribution increases with the amount of vinyl aromatic monomer, suchas styrene, being incorporated into the rubber. However, if this ratiois too high, the vinyl content of the polymer will increase and thereaction rate will be slower.

[0043] The sodium salts of glycol ethers that can be used in theinitiator systems of this invention are typically of the structuralformula:

Na—(O—(CH₂)_(n))_(m)—O—(CH₂)_(x)—CH₃

[0044] wherein Na represents sodium; wherein n represents an integerfrom 2 to 10; wherein m represents an integer from 1 to 6; and wherein xrepresents an integer from 1 to 12. In is preferred for n to representan integer from 2 to about 4, for m to represent an integer from 2 to 8,and for x to represent an integer from 1 to 8. It is more preferred forn to represent an integer from 2 to 3, for m to represent an integerfrom 2 to 4, and for x to represent an integer from 1 to 4.

[0045] A highly preferred salt is the sodium salt of di(ethyleneglycol)ethyl ether which is of the structural formula:

Na—O—CH₂—CH₂—O—CH₂—CH₂—O—CH₂—CH₃

[0046] Other highly preferred group salts include sodium salts oftri(ethyleneglycol) ethyl ethers and sodium salts oftetra(ethyleneglycol) ethyl ethers.

[0047] The molar ratio of the lithium initiator to the sodium salt ofthe glycol ether will typically be within the range of about 0.1:1 to20:1. The molar ratio of the lithium initiator to the sodium salt of theglycol ether will preferably be within the range of about 0.5:1 to about15:1. The molar ratio of the lithium initiator to the sodium salt of theglycol ether will more preferably be within the range of about 2:1 toabout 4:1.

[0048] After the polymerization has been completed, the living rubberypolymer can optionally be coupled with a suitable coupling agent, suchas a tin tetrahalide or a silicon tetrahalide. The rubbery polymer isthen recovered from the organic solvent. The polydiene rubber can berecovered from the organic solvent and residue by any means, such asdecantation, filtration, centrification and the like. It is oftendesirable to precipitate the rubbery polymer from the organic solvent bythe addition of lower alcohols containing from about 1 to about 4 carbonatoms to the polymer solution. Suitable lower alcohols for precipitationof the rubbery polymer from the polymer cement include methanol,ethanol, isopropyl alcohol, normal-propyl alcohol and t-butyl alcohol.The utilization of lower alcohols to precipitate the rubber from thepolymer cement also “kills” the living polymer by inactivating lithiumend groups After the rubbery polymer is recovered from the solution,steam stripping can be employed to reduce the level of volatile organiccompounds in the polymer. The inert solvent and residual monomer canthen be recycled for subsequent polymerization.

[0049] There are valuable benefits associated with utilizing polydienerubber made with the initiator systems of this invention in tire treadcompounds. For instance, tire tread compounds with improved tractioncharacteristics can be made by blending the styrene-isoprene rubberhaving a low vinyl content and a random distribution of styrene repeatunits into tire tread compounds. This styrene-isoprene rubber willtypically have a bound styrene content which is within the range ofabout 5 weight percent to about 60 weight percent and a glass transitiontemperature that is within the range of about −70° C. to about 10° C.The styrene-isoprene rubber will more typically have a bound styrenecontent which is within the range of about 30 weight percent to about 50weight percent and a glass transition temperature that is within therange of about −45° C. to about −15° C. The glass transition temperatureof the styrene-isoprene polymer will vary with its bound styrenecontent. As a general rule, the glass transition temperature of thestyrene-isoprene polymer is raised by 1° C. for every 1% increase in thebound styrene content of the polymer.

[0050] The traction characteristics of a tire tread compound can beimproved by simply blending up to about 50 weight percent of thestyrene-isoprene rubber into a conventional tire tread compound. Forexample, the styrene-isoprene rubber can be used as a replacement for3,4-polyisoprene which is sometimes used in tire tread compounds toimprove traction characteristics. Blends of the styrene-isoprene rubberwith high cis-1,4-polybutadiene rubber having a glass transitiontemperature that is within the range of about −110° C. to about −100° C.and/or low cis-1,4-polybutadine rubber having a glass transitiontemperature that is within the range of about −70° C. to about −30° C.have proven to be beneficial for improving tire traction characteristicswithout compromising the rolling resistance or tread-wear of the tire.Such blends will typically contain from about 5 phr (parts per 100 partsby weight of rubber) to 50 phr of the styrene-isoprene rubber and 50 phrto 95 phr of the low cis-1,4-polybutadiene rubber and/or the highcis-1,4-polybutadiene rubber. Such blends will more typically containfrom about 20 phr to 40 phr of the styrene-isoprene rubber and 60 phr to80 phr of the low cis-1,4-polybutadiene rubber and/or the highcis-1,4-polybutadiene rubber.

[0051] Tire tread compounds can also be made by blending thestyrene-isoprene rubber with natural rubber. Such a tire tread compoundcan be made by blending about 30 phr to about 70 phr of thestyrene-isoprene rubber with about 30 phr to 70 phr of natural rubber.Styrene-butadiene rubber can also be included in such tire treadcompounds. For instance, a tire tread compound can be made by blendingabout 5 phr to about 50 phr of the styrene-isoprene rubber, about 5 phrto about 50 phr of natural rubber, and about 5 phr to about 50 phr ofstyrene-butadiene rubber. The styrene-butadiene rubber included in suchblends can be made by solution or emulsion polymerization.

[0052] Such polydiene rubber blends can be compounded utilizingconventional ingredients and standard techniques. For instance,styrene-isoprene rubber blends will typically be mixed with carbon blackand/or silica, sulfur, fillers, accelerators, oils, waxes, scorchinhibiting agents, and processing aids. In most cases, thestyrene-isoprene rubber blends will be compounded with sulfur and/or asulfur containing compound, at least one filler, at least oneaccelerator, at least one antidegradant, at least one processing oil,zinc oxide, optionally a tackifier resin, optionally a reinforcingresin, optionally one or more fatty acids, optionally a peptizer andoptionally one or more scorch inhibiting agents. Such blends willnormally contain from about 0.5 to 5 phr (parts per hundred parts ofrubber by weight) of sulfur and/or a sulfur containing compound with 1phr to 2.5 phr being preferred. It may be desirable to utilize insolublesulfur in cases where bloom is a problem.

[0053] Normally from 10 to 150 phr of at least one filler will beutilized in the blend with 30 to 80 phr being preferred. In most casesat least some carbon black will be utilized in the filler. The fillercan, of course, be comprised totally of carbon black. Silica can beincluded in the filler to improve tear resistance and heat build up.Clays and/or talc can be included in the filler to reduce cost. Theblend will also normally include from 0.1 to 2.5 phr of at least oneaccelerator with 0.2 to 1.5 phr being preferred. Antidegradants, such asantioxidants and antiozonants, will generally be included in the treadcompound blend in amounts ranging from 0.25 to 10 phr with amounts inthe range of 1 to 5 phr being preferred. Processing oils will generallybe included in the blend in amounts ranging from 2 to 100 phr withamounts ranging from 5 to 50 phr being preferred. The polybutadieneblends of this invention will also normally contain from 0.5 to 10 phrof zinc oxide with 1 to 5 phr being preferred. These blends canoptionally contain from 0 to 10 phr of tackifier resins, 0 to 10 phr ofreinforcing resins, 1 to 10 phr of fatty acids, 0 to 2.5 phr ofpeptizers, and 0 to 1 phr of scorch inhibiting agents.

[0054] To fully realize the total advantages of such styrene-isoprenerubber blends, silica will normally be included in the tread rubberformulation. The processing of the styrene-isoprene rubber blend isnormally conducted in the presence of a sulfur containing organosiliconcompound to realize maximum benefits. Examples of suitable sulfurcontaining organosilicon compounds are of the formula:

Z-Alk-S_(n)-Alk-Z  (I)

[0055] in which Z is selected from the group consisting of

[0056] where R¹ is an alkyl group of 1 to 4 carbon atoms, cyclohexyl orphenyl; wherein R² is alkoxy of 1 to 8 carbon atoms, or cycloalkoxy of 5to 8 carbon atoms; and wherein Alk is a divalent hydrocarbon of 1 to 18carbon atoms and n is an integer of 2 to 8.

[0057] Specific examples of sulfur containing organosilicon compoundswhich may be used in accordance with the present invention include:3,3′-bis(trimethoxysilylpropyl) disulfide,3,3′-bis(triethoxysilylpropyl) tetrasulfide,3,3′-bis(triethoxysilylpropyl) octasulfide,3,3′-bis(trimethoxysilylpropyl) tetrasulfide,2,2′-bis(triethoxysilylethyl) tetrasulfide,3,3′-bis(trimethoxysilylpropyl) trisulfide,3,3′-bis(triethoxysilylpropyl) trisulfide,3,3′-bis(tributoxysilylpropyl) disulfide,3,3′-bis(trimethoxysilylpropyl) hexasulfide,3,3′-bis(trimethoxysilylpropyl) octasulfide,3,3′-bis(trioctoxysilylpropyl) tetrasulfide,3,3′-bis(trihexoxysilylpropyl) disulfide,3,3′-bis(tri-2″-ethylhexoxysilylpropyl) trisulfide,3,3′-bis(triisooctoxysilylpropyl) tetrasulfide,3,3′-bis(tri-t-butoxysilylpropyl) disulfide, 2,2′-bis(methoxy diethoxysilyl ethyl) tetrasulfide, 2,2′-bis(tripropoxysilylethyl) pentasulfide,3,3′-bis(tricyclonexoxysilylpropyl) tetrasulfide,3,3′-bis(tricyclopentoxysilylpropyl) trisulfide,2,2′-bis(tri-2″-methylcyclohexoxysilylethyl) tetrasulfide,bis(trimethoxysilylmethyl) tetrasulfide, 3-methoxy ethoxy propoxysilyl3′-diethoxybutoxy-silylpropyltetrasulfide, 2,2′-bis(dimethylmethoxysilylethyl) disulfide, 2,2′-bis(dimethyl sec.butoxysilylethyl)trisulfide, 3,3′-bis(methyl butylethoxysilylpropyl) tetrasulfide,3,3′-bis(di t-butylmethoxysilylpropyl) tetrasulfide, 2,2′-bis(phenylmethyl methoxysilylethyl) trisulfide, 3,3′-bis(diphenylisopropoxysilylpropyl) tetrasulfide, 3,3′-bis(diphenylcyclohexoxysilylpropyl) disulfide, 3,3′-bis(dimethylethylmercaptosilylpropyl) tetrasulfide, 2,2′-bis(methyldimethoxysilylethyl) trisulfide, 2,2′-bis(methylethoxypropoxysilylethyl) tetrasulfide, 3,3′-bis(diethylmethoxysilylpropyl) tetrasulfide, 3,3′-bis(ethyl di-sec.butoxysilylpropyl) disulfide, 3,3′-bis(propyl diethoxysilylpropyl)disulfide, 3,3′-bis(butyl dimethoxysilylpropyl) trisulfide,3,3′-bis(phenyl dimethoxysilylpropyl) tetrasulfide, 3-phenylethoxybutoxysilyl 3′-trimethoxysilylpropyl tetrasulfide,4,4′-bis(trimethoxysilylbutyl) tetrasulfide,6,6′-bis(triethoxysilylhexyl) tetrasulfide,12,12′-bis(triisopropoxysilyl dodecyl) disulfide,18,18′-bis(trimethoxysilyloctadecyl) tetrasulfide,18,18′-bis(tripropoxysilyloctadecenyl) tetrasulfide,4,4′-bis(trimethoxysilyl-buten-2-yl) tetrasulfide,4,4′-bis(trimethoxysilylcyclohexylene) tetrasulfide,5,5′-bis(dimethoxymethylsilylpentyl) trisulfide,3,3′-bis(trimethoxysilyl-2-methylpropyl) tetrasulfide,3,3′-bis(dimethoxyphenylsilyl-2-methylpropyl) disulfide.

[0058] The preferred sulfur containing organosilicon compounds are the3,3′-bis(trimethoxy or triethoxy silylpropyl) sulfides. The mostpreferred compound is 3,3′-bis(triethoxysilylpropyl) tetrasulfide.Therefore as to formula I, preferably Z is

[0059] where R² is an alkoxy of 2 to 4 carbon atoms, with 2 carbon atomsbeing particularly preferred; Alk is a divalent hydrocarbon of 2 to 4carbon atoms with 3 carbon atoms being particularly preferred; and n isan integer of from 3 to 5 with 4 being particularly preferred.

[0060] The amount of the sulfur containing organosilicon compound offormula I in a rubber composition will vary depending on the level ofsilica that is used. Generally speaking, the amount of the compound offormula I will range from about 0.01 to about 1.0 parts by weight perpart by weight of the silica. Preferably, the amount will range fromabout 0.02 to about 0.4 parts by weight per part by weight of thesilica. More preferably the amount of the compound of formula I willrange from about 0.05 to about 0.25 parts by weight per part by weightof the silica.

[0061] In addition to the sulfur containing organosilicon, the rubbercomposition should contain a sufficient amount of silica, and carbonblack, if used, to contribute a reasonably high modulus and highresistance to tear. The silica filler may be added in amounts rangingfrom about 10 phr to about 250 phr. Preferably, the silica is present inan amount ranging from about 15 phr to about 80 phr. If carbon black isalso present, the amount of carbon black, if used, may vary. Generallyspeaking, the amount of carbon black will vary from about 5 phr to about80 phr. Preferably, the amount of carbon black will range from about 10phr to about 40 phr. It is to be appreciated that the silica coupler maybe used in conjunction with a carbon black, namely pre-mixed with acarbon black prior to addition to the rubber composition, and suchcarbon black is to be included in the aforesaid amount of carbon blackfor the rubber composition formulation. In any case, the total quantityof silica and carbon black will be at least about 30 phr. The combinedweight of the silica and carbon black, as hereinbefore referenced, maybe as low as about 30 phr, but is preferably from about 45 to about 130phr.

[0062] The commonly employed siliceous pigments used in rubbercompounding applications can be used as the silica. For instance thesilica can include pyrogenic and precipitated siliceous pigments(silica), although precipitate silicas are preferred. The siliceouspigments preferably employed in this invention are precipitated silicassuch as, for example, those obtained by the acidification of a solublesilicate, e.g., sodium silicate.

[0063] Such silicas might be characterized, for example, by having a BETsurface area, as measured using nitrogen gas, preferably in the range ofabout 40 to about 600, and more usually in a range of about 50 to about300 square meters per gram. The BET method of measuring surface area isdescribed in the Journal of the American Chemical Society, Volume 60,page 304 (1930).

[0064] The silica may also be typically characterized by having adibutylphthalate (DBP) absorption value in a range of about 100 to about400, and more usually about 150 to about 300. The silica might beexpected to have an average ultimate particle size, for example, in therange of 0.01 to 0.05 micron as determined by the electron microscope,although the silica particles may be even smaller, or possibly larger,in size.

[0065] Various commercially available silicas may be considered for usein this invention such as, only for example herein, and withoutlimitation, silicas commercially available from PPG Industries under theHi-Sil trademark with designations 210, 243, etc; silicas available fromRhone-Poulenc, with, for example, designations of Z1165MP and Z165GR andsilicas available from Degussa AG with, for example, designations VN2and VN3.

[0066] Tire tread formulations which include silica and an organosiliconcompound will typically be mixed utilizing a thermomechanical mixingtechnique. The mixing of the tire tread rubber formulation can beaccomplished by methods known to those having skill in the rubber mixingart. For example the ingredients are typically mixed in at least twostages, namely at least one non-productive stage followed by aproductive mix stage. The final curatives including sulfur vulcanizingagents are typically mixed in the final stage which is conventionallycalled the “productive” mix stage in which the mixing typically occursat a temperature, or ultimate temperature, lower than the mixtemperature(s) than the preceding non-productive mix stage(s). Therubber, silica and sulfur containing organosilicon, and carbon black ifused, are mixed in one or more non-productive mix stages. The terms“non-productive” and “productive” mix stages are well known to thosehaving skill in the rubber mixing art. The sulfur vulcanizable rubbercomposition containing the sulfur containing organosilicon compound,vulcanizable rubber and generally at least part of the silica should besubjected to a thermomechanical mixing step. The thermomechanical mixingstep generally comprises a mechanical working in a mixer or extruder fora period of time suitable in order to produce a rubber temperaturebetween 140° C. and 190° C. The appropriate duration of thethermomechanical working varies as a function of the operatingconditions and the volume and nature of the components. For example, thethermomechanical working may be for a duration of time which is withinthe range of about 2 minutes to about 20 minutes. It will normally bepreferred for the rubber to reach a temperature which is within therange of about 145° C. to about 180° C. and to be maintained at saidtemperature for a period of time which is within the range of about 4minutes to about 12 minutes. It will normally be more preferred for therubber to reach a temperature which is within the range of about 155° C.to about 170° C. and to be maintained at said temperature for a periodof time which is within the range of about 5 minutes to about 10minutes.

[0067] Tire tread compounds made using such styrene-isoprene rubbercontaining blends can be used in tire treads in conjunction withordinary tire manufacturing techniques. Tires are built utilizingstandard procedures with the styrene-isoprene rubber simply beingincluded in the blend used as the tread rubber. After the tire has beenbuilt with the styrene-isoprene rubber containing blend, it can bevulcanized using a normal tire cure cycle. Tires made in accordance withthis invention can be cured over a wide temperature range. However, itis generally preferred for the tires to be cured at a temperatureranging from about 132° C. (270° F.) to about 166° C. (330° F.) It ismore typical for the tires of this invention to be cured at atemperature ranging from about 143° C. (290° F.) to about 154° C. (310°F.). It is generally preferred for the cure cycle used to vulcanize thetires to have a duration of about 10 to about 20 minutes with a curecycle of about 12 to about 18 minutes being most preferred.

[0068] This invention is illustrated by the following examples that aremerely for the purpose of illustration and are not to be regarded aslimiting the scope of the invention or the manner in which it can bepracticed. Unless specifically indicated otherwise, all parts andpercentages are given by weight.

EXAMPLE 1

[0069] In a one-gallon (3.785 liter) glass bowl reactor equipped with amechanical stirrer and temperature control via cooling water and lowpressure steam, polymerization of the isoprene monomer was carried out.The reactor was charged with 2000 grams of premix, which contains 20%monomer dissolved in hexane solvent. The reactor contents were thenheated to 65° C. At 65° C., a catalyst system consisting of a 0.75/1ratio of sodium dodecylbenzene sulfonate (SDBS) to n-butyllithium(n-BuLi) was added to the reactor to initiate polymerization. Sampleswere taken over the course of the reaction to determine monomerconversion, which was presented as a function of time. The reaction wasshort-stopped with denatured ethanol, and antioxidant was added to thepolymer. The polymer was dried for several days in an oven to make sureall solvent had evaporated.

EXAMPLE 2

[0070] Using the same reactor setup as Example 1, the copolymerizationof styrene and isoprene was carried out. In this experiment a polymercontaining 10% styrene and 90% isoprene was synthesized (10/90 SIR).Therefore, 200 grams of 20% styrene premix and 1800 grams of 20%isoprene premix were charged to the reactor. Once again, the reactiontemperature was 65° C. and a ratio of 0.75/1 SDBS to n-BuLi was used toinitiate polymerization. A target molecular weight of 150,000 was used.Samples were taken over time to monitor both styrene and isoprenemonomer conversion as a function of time, monomer conversion as afunction of total conversion, and the copolymer composition as afunction of total conversion. Ethanol was used to short-stop thereaction and antioxidant was added upon completion. The polymer was thendried for several days in an oven to make sure all solvent had beenevaporated.

EXAMPLES 3-7

[0071] Using the same procedure as described in Example 2, a series ofSIR copolymers were synthesized. The series consisted of 20 to 60percent styrene (20/80, 30/70, 40/60, 50/50 and 60/40 SIR). Therefore,the styrene and isoprene premixes were added to obtain the desiredcopolymer composition. The glass transition temperature was controlledby the amount of styrene in the copolymer. All final products weresoluble in hexane solvent. Table 1 shows all the polymer characteristicsfor this series, including Example 2 and Example 8. The polymer glasstransition temperature (Tg) was determined using differential scanningcalorimetry techniques (DSC), while the -number averave molecular weight(Mn) and polydispersity (PDI) were obtained through gel permeationchromatography (GPC), and the copolymer microstructure was found throughproton NMR techniques. Table 2 gives the styrene sequence distributionas determined through ozonolysis techniques. Ozonolysis techniques areneeded because it is difficult to obtain the amount of block styrene instyrene/isoprene copolymers through traditional NMR techniques.

EXAMPLE 8

[0072] Using a similar procedure as described in Example 2, a copolymerof 70% styrene and 30% isoprene was synthesized (70/30 SIR). Here theonly difference in procedure was how the reactor was initially chargedwith premix. Approximately 1050 grams of styrene premix and 450 grams ofisoprene premix along with 500 grams of cyclohexane were added to thereactor. This was then heated, and the catalyst was injected. Thecyclohexane helped to keep the copolymer fully in solution. Withoutcyclohexane, the 70/30 SIR appeared to be a colloidal suspension. TABLE1 Polymer characteristics for SIR copolymers presented in Examples 2-8.Tg Example (° C.) Mn PDI % Styrene % 1, 4 PI % 3, 4 PI 2 −56.64 446,0001.14  9.1 81.7 9.2 3 −48.06 393,000 1.25 19.0 72.7 8.3 4 −38.70 408,0001.22 27.4 64.0 8.6 5 −27.05 435,000 1.17 40.1 50.0 9.9 6 −15.99 493,0001.20 49.0 42.7 8.3 7 −3.21 500,000 1.15 57.2 35.1 7.7 8 21.08 562,0001.17 67.1 27.1 5.8

[0073] TABLE 2 Styrene Sequence Distribution for SIR in Examples 2-8.Experiment Number Sequence 2 3 4 5 6 7 8  1S 58.4 47.3 36.8 20.0 16.215.3 12.5  2S 33.5 34.5 35.0 26.0 23.8 20.3 16.1  3S 8.1 14.9 19.3 21.020.5 16.3 14.0  4S 3.3 5.5 15.0 14.8 12.9 11.8  5S 3.4 9.5 10.7 11.111.1  6S 5.5 6.9 9.6 10.3  7S 2.3 3.4 3.6 5.2  8S 0.7 2.3 3.8 5.2  9S1.0 0.8 1.4 10S 0.4 2.2 2.8 11S 1.5 1.9 12S 1.0 2.4 13S 0.6 1.8 14S 0.41.2 15S 0.2 0.9 16S 0.1 0.5 17S 0.1 0.4 18S 0.1 0.2 19S 0.1 0.1 20S 0.121S 0.1

EXAMPLE 9

[0074] Using the reactor set-up in Example 1, a 45/55 styrene/isoprenecopolymer was made via sodium mentholate (SMT). Approximately 900 g ofstyrene premix and 1100 grams isoprene premix, both in hexane solvent,were added to the reactor. To initiate polymerization a ratio of 0.25/1SMT to n-BuLi was added to the reactor at a temperature of 65° C. Aglass transition temperature (Tg) of −17.4° C. resulted. The Mn of thepolymer was 506,000 g/mol (a target Mn of 450,000 was used).

EXAMPLE 10

[0075] Using the reactor set-up in Example 1, a 45/55 styrene/isoprenecopolymer was made via SDBS and3-(T-butyldimethylsilyloxy)-2,2-dimethyl-1-propyllithium (PFI-2), afunctionalized initiator. Approximately 900 g of styrene premix and 1100grams isoprene premix, both in hexane solvent, were added to thereactor. To initiate polymerization a ratio of 0.5/1 SDBS to PFI-2 wasadded to the reactor at a temperature of 65° C. A Tg of −19.83° C.resulted. The Mn of the polymer was 433,900 g/mol (a target Mn of225,000 was used).

EXAMPLE 11

[0076] Using the reactor set-up in Example 1, a 45/55 styrene/isoprenecopolymer was made via sodium salt of di(ethylene glycol) methyl ether(NaDEGME) and n-BuLi. Approximately 900 g of styrene premix and 1100grams isoprene premix, both in hexane solvent, were added to thereactor. To initiate polymerization a ratio of 0.25/1 NaDEGME to n-BuLiwas added to the reactor at a temperature of 65° C. A Tg of −30.93° C.resulted. The Mn of the polymer was 298,600 g/mol (a target Mn of200,000 was used).

EXAMPLE 12

[0077] Using the reactor set-up in Example 1, a 45/55 styrene/isoprenecopolymer was made via sodium salt of di(ethylene glycol) dietheyl ether(NaDEGDEE) and n-BuLi. Approximately 900 grams of styrene premix and1100 g isoprene premix, both in hexane solvent, were added to thereactor. To initiate polymerization a ratio of 0.25/1 NaDEGDEE to n-BuLiwas added to the reactor at a temperature of 90° C. A Tg of −16.29° C.resulted. The Mn of the polymer was 378,500 g/mole (a target Mn of250,000 was used).

EXAMPLE 13

[0078] Using the reactor set-up in Example 1, a 45/55 styrene/isoprenecopolymer was made via sodium salt of tri(propylene glycol) methyl ether(NaTPGME) and n-BuLi. Approximately 900 grams of styrene premix and 100g isoprene premix, both in hexane solvent, were added to the reactor. Toinitiate polymerization a ratio of 0.25/1 NaTPGME to n-BuLi was added tothe reactor at a temperature of 90° C. A glass transition temperature of−13.13° C. resulted. The number averave molecular weight (Mn) of thepolymer was 328,700 grams/mole (a target Mn of 250,000 was used).

[0079] Variations in the present invention are possible in light of thedescription of it provided herein. It is, therefore, to be understoodthat changes can be made in the particular embodiments described whichwill be within the full intended scope of the invention as defined bythe following appended claims.

What is claimed is:
 1. A process for preparing a rubbery polymer havinga low vinyl content which comprises: polymerizing at least one dienemonomer with a lithium initiator at a temperature which is within therange of about 0° C. to about 180° C. in the presence of a memberselected from the group consisting of (1) a sodium alkoxide, (2) asodium salt of a sulfonic acid, and (3) a sodium salt of a glycol ether,and wherein the process is conducted in the absence of polar modifiers.2. a process for preparing a styrene-isoprene rubber having a low vinylcontent and a random distribution of repeat units that are derived fromstyrene which comprises: copolymerizing styrene and isoprene with alithium initiator at a temperature which is within the range of about 0°C. to about 180° C. in the presence of a member selected from the groupconsisting of (1) a sodium alkoxide, (2) a sodium salt of a sulfonicacid, and (3) a sodium salt of a glycol ether, and wherein the processis conducted in the absence of polar modifiers.
 3. An initiator systemwhich is comprised of (a) a lithium initiator and (b) a member selectedfrom the group consisting of (1) a sodium alkoxide, (2) a sodium salt ofa sulfonic acid, and (3) a sodium salt of a glycol ether, wherein saidinitiator system is void of polar modifiers.
 4. A process as specifiedin claim 2 wherein a sodium alkoxide is present.
 5. A process asspecified in claim 4 wherein the molar ratio of the sodium alkoxide tothe lithium initiator is within the range of about 0.05:1 to about 10:1.6. A process as specified in claim 4 wherein the molar ratio of sodiumalkoxide to the lithium initiator is within the range of about 0.2:1 toabout 3:1.
 7. A process as specified in claim 11 wherein the molar ratioof the sodium alkoxide to the lithium initiator is within the range ofabout 0.05:1 to about 10:1.
 8. A process as specified in claim 5 whereinthe lithium initiator is an alkyl lithium compound.
 9. A process asspecified in claim 8 wherein the polymerization is conducted at atemperature which is within the range of about 40° C. to about 90° C.10. A process as specified in claim 9 wherein said polymerization isconducted in an inert organic solvent.
 11. A process as specified inclaim 10 wherein the sodium alkoxide is sodium t-amyloxide.
 12. Aprocess as specified in claim 10 wherein the sodium alkoxide is of theformula NaOR wherein R represents an alkyl group containing from about 2to about 12 carbon atoms.
 13. A process as specified in claim 12 whereinR represents an alkyl group containing from about 3 to about 8 carbonatoms.
 14. A process as specified in claim 12 wherein R represents analkyl group containing from about 4 to about 6 carbon atoms.
 15. Aprocess as specified in claim 13 wherein the molar ratio of the sodiumalkoxide to the lithium initiator is within the range of about 0.2:1 toabout 3:1.
 16. A process as specified in claim 15 wherein the lithiuminitiator is n-butyl lithium.
 17. A process as specified in claim 16wherein the polymerization is conducted at a temperature which is withinthe range of about 60° C. to about 90° C.
 18. A process as specified inclaim 2 wherein a sodium salt of a sulfonic acid is present, and whereinthe process is conducted in the absence of water.
 19. A process asspecified in claim 2 wherein a sodium salt of a glycol ether is present.20. A process as specified in claim 2 wherein the sodium salt of aglycol ether is the sodium salt of (ethylene glycol) ethyl ether.